I. Field
The following description relates generally to wireless communications, and more particularly to methods and apparatuses for facilitating a hand-in of user equipment to femto cells.
II. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A MIMO system supports a time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the access point to extract transmit beamforming gain on the forward link when multiple antennas are available at the access point.
In cellular networks, Macro Node Bs (MNBs) provide connectivity and coverage to a large number of users over a certain geographical area. A macro network deployment is carefully planned, designed and implemented to offer good coverage over the geographical region. While, such a careful planning is necessary, it however, cannot accommodate channel characteristics such as fading, multipath, shadowing, etc. especially in indoor environments. Indoor users, therefore, often face coverage issues (call outages, quality degradation) resulting in poor user experience.
Miniaturized base stations known as femto cells or Home Node Bs (HNBs) are expected to address this issue by extending cellular coverage inside buildings. Femto cells are a new class of base stations, which may be installed in a user's home and provide indoor wireless coverage to mobile units using existing broadband Internet connections.
However, an unplanned deployment of large numbers of HNBs will likely create several challenges that need addressing. For instance, when a mobile user gets close to a femto cell (e.g., cellular subscriber coming home), it may be desirable to enable a handover to that particular femto cell. It may be difficult though to uniquely identify the femto cell to facilitate such a handover. Typically in a macro network, identification of MNBs is achieved by assigning a unique primary scrambling code (PSC) to an MNB in a certain coverage area. However, this is not feasible in femto cell deployments due to the limited number of PSCs that are allocated and reused and small scale coverage of HNBs compared to MNBs. Therefore, simply using PSCs alone for HNB identification would result in ambiguities during an active hand-in procedure, wherein false HNB identification would result in severe network performance degradation.
It should also be noted that, upon relocating a user equipment (UE) in a CELL_DCH (Cell Dedicated Channel) state from a UMTS macro cell to an HNB cell, a combined SRNS (Serving Radio Network Subsystem) Relocation with hard hand-over is required, due to the lack of an Iur connection. For identifying the target of this relocation, the SRNC (Serving Radio Network Controller) can currently rely on either UE measurement reports and/or implicit OA&M (operations, administration, and management) mapping measurements to a target RNC (Radio Network Controller) to use in SRNS Relocation. Measurements currently only optionally provide the 28-bit global cell-id. In fact, the RANAP (Radio Access Network Application Part) measurement procedure assumes that the RNS (Radio Network Subsystem) never requests cell id reporting by the UE. Other measurable parameters (like PSC of the measured cell) might aid in narrowing down the candidate list of cells whose measurement are taken, but cannot guarantee the identification of the target HNB in an unrestricted HNB deployment. This leads to inefficiencies and ambiguities in RANAP signaling, as multiple candidate target HNBs may have to be prepared for handover. This problem is commonly known as the “PSC Confusion” problem.
Accordingly, it would be desirable to develop a method and apparatus for facilitating a hand-in of user equipment to femto cells, wherein the PSC confusion problem is resolved. The above-described deficiencies of current wireless communication systems are merely intended to provide an overview of some of the problems of conventional systems, and are not intended to be exhaustive. Other problems with conventional systems and corresponding benefits of the various non-limiting embodiments described herein may become further apparent upon review of the following description.